Reed Canary Grass Removal in a Protected Wetland
A land trust manages a 12-hectare wetland that supports a state-protected chorus frog. Reed canary grass (RCG) covers 4 ha and is spreading. Options: (A) broadcast herbicide in spring, (B) mow and tarp for two seasons, (C) late-summer flooding for 6 weeks. The frog breeds March–May in shallow water; larvae need 8 weeks. Herbicide label restricts application within 15 m of water and during frog breeding. Mowing requires heavy equipment and may compact soil; tarping costs $18,000/ha and kills non-target plants. Flooding needs a water right and may release sediment downstream. The trust has $60,000 and a 3-year window. Monitoring budget is $8,000. A local watershed group has threatened to appeal any herbicide permit. The board wants a decision that is defensible to regulators and does not sacrifice the frog population.
1. Recommend a strategy and justify it using ecological and regulatory constraints. State one tradeoff you accept.
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Recommend a staged mow-and-tarp treatment on a prioritized 2 ha subset, not broadcast herbicide. Herbicide is constrained within 15 m of water and during breeding, and a permit appeal would delay action. Flooding depends on a water right and risks downstream sediment. Mowing and tarping avoids direct chemical exposure to the frog and avoids sediment release, but at $18,000/ha only 2 ha fit the first-year budget. Prioritize the 2 ha with the highest RCG cover and greatest connectivity to intact habitat. Treat after larval metamorphosis, roughly late summer, to avoid breeding and larval stages. Accept the tradeoff of slower containment: the remaining 2 ha will spread unless treated in later years, so the 3-year plan must include sequential treatment and native seeding. This staged approach is defensible because it is timed around frog life history and avoids the regulatory vulnerability of a herbicide permit.
2. Design a monitoring plan that could distinguish treatment failure from natural variation. Include response variables, controls, and timing.
Read the worked answer
Use a before-after-control-impact design. Establish permanent transects in treated and untreated reference plots matched for hydrology and initial RCG cover. Response variables: RCG percent cover and stem density, native forb and sedge cover, bare ground, frog egg-mass counts, larval survival, and water turbidity downstream. Collect baseline data in spring before treatment, then at 6 weeks and annually for at least 3 years. Randomize plot locations and include unmanipulated controls to account for weather-driven variation. Treatment failure would appear as RCG cover in treated plots returning to or exceeding baseline while controls remain stable; natural variation would affect both treated and control plots similarly. Include soil compaction measurements if heavy equipment is used.
3. The RCG seed bank remains viable for more than five years. Explain how this changes the expected outcome and the follow-up budget.
Read the worked answer
A persistent seed bank means one removal will not control RCG. Killing adult stems will trigger a seedling flush from buried seed, so the site may look clean for one season and then reinvade. The expected outcome is a multi-year depletion program, not a single treatment. Budget must cover repeated annual tarping or spot treatment for at least 5–7 years, plus native seeding to occupy niches and monitoring for seedling recruitment. The $60,000 should be allocated as a multi-year commitment rather than spent entirely in year one. Without follow-up, the initial investment will fail and the board will have created disturbance that favors RCG.